(1) Field of the Invention
The present invention relates to a novel liquid peroxide composition and a process for the preparation thereof. More particularly, the invention relates to a liquid peroxide composition valuable as a cross-linking agent for a high polymer for electric insulation, and a process for the preparation thereof.
(2) Description of the Prior Art
Electrically insulating layers for wires, cables and the like are ordinarily formed by extruding on a conductor a composition comprising high-pressure polyethylene and an appropriate amount of an organic peroxide cross-linking agent to form a coating on the conductor and cross-linking the coated composition. In order to carry out cross-linking of polyethylene at high efficiency at the cross-linking step while preventing decomposition of the peroxide cross-linking agent at the extruding and coating step, dicumyl peroxide (hereinafter abbreviated to "DCP") which has excellent properties as the organic peroxide cross-linking agent and is cheap is mainly used in this field. However, even DCP still involves problems to be solved or defects to be eliminated. At the step of kneading polyethylene with DCP, the use of an extruder is ordinarily preferred from the viewpoint of the operation efficiency, but when the extruder is used at the kneading step, in order to obtain a homogeneous composition, it is necessary to feed DCP at a constant speed. For this purpose, DCP which is normally in the form of a solid inferior in the metering property should be molten to render it liquid. This requires provision of a particular device for melting DCP and furthermore, this results in a disadvantage that since DCP is maintained in the high-temperature molten state, loss of DCP is caused by decomposition and a special care should be paid to maintenance of the safety. Furthermore, when solid DCP is handled, incorporation of different matter is hardly avoided, and different matter having bad influences on the quality of the insulating layer should be removed in advance. Therefore, such troublesome operation as filtration after melting should inevitably be conducted.
Of course, liquid peroxides are known in the art. However, known liquid peroxides such as .alpha.,.alpha.-dimethylbenzyl(.alpha.,.alpha.-dimethyl-p-isopropylbenzyl) peroxide disclosed in the specifications of U.S. Pat. No. 2,819,256 and U.S. Pat. No. 2,826,570 are still insufficient and defective in that the gel proportion of a cross-linked polymer obtained by incorporating such liquid peroxide into a polymer so that an active oxygen amount is constant is much lower than the gel proportion attained by DCP. In short, these known liquid peroxides are still unsatisfactory in the cross-linking efficiency.